1. Field of the Invention
The present invention relates to an assembly for tilting a wafer platen of an ion implanter for manufacturing semiconductor devices. More particularly, the present invention relates to the connection between a rotating body and a shaft of a transmission mechanism for transmitting a drive force to the wafer platen.
2. Description of the Related Art
Ion implantation is a semiconductor manufacturing technique in which impurities are ionized, accelerated, and implanted into a desired area of a semiconductor substrate. Furthermore, ion implantation allows the impurities to be selectively implanted with accurate control. In addition, ion implantation can be performed with excellent process reproducibility and process uniformity. Therefore, the ion implantation process lends itself well to the mass-production of highly integrated semiconductor devices. Accordingly, the role of ion implantation in the semiconductor manufacturing process is continuing to gain in importance.
For maximum efficacy of the implantation process, it is known that a semiconductor wafer should be oriented at a predetermined angle relative to the ion beam. However, the wafer may be supported unstably while being tilted. Facility inspections have uncovered problems in the attachment of a drive shaft to a rotating arm controlling the Y-axis tilt of the wafer, and the attachment of a rotary shaft to a pulley controlling the X-axis tilt of the wafer. When these problems exist, the impurities are implanted to different depths in various portions of the wafer instead of being implanted to a uniform depth. Thus, these problems adversely affect the reliability of the facilities and the productivity of the manufacturing process.
The orienting of a wafer platen of the ion implanter will now be briefly described with reference to FIG. 5. The wafer platen 75 can be moved in the direction of arrows Axe2x80x3 for controlling the X-axis tilt and in the direction of arrows Bxe2x80x2 for controlling the Y-axis tilt.
FIG. 1 illustrates a connecting system for controlling the Y-axis tilt of a wafer platen in an implanter according to the prior art. Referring to FIG. 1, the connecting system includes a drive shaft 6, a rotating arm 10, ferrules 8, a bracket 14, and screws 12. The drive shaft 6 is rotated by a drive motor 2. Reference numeral 4 designates a plate to which the motor 2 is fixed. The rotating arm 10 is engaged with the drive shaft 6 so as to be rotated by the same. The ferrules 8 are positioned between the rotating arm 10 and the drive shaft 6. The bracket 14 tightens the ferrules 8 and holds the drive shaft 6. The screws 12 fix the bracket 14 onto the side of the rotating arm 10.
The ferrules 8 have alternating flat and angled outer edges, and are disposed on the outside of the drive shaft 6. Because the bracket 14 is fixed on the rotating arm 10, the ferrules 8 transmit the rotary force of the drive shaft 6 to the rotating arm 10. However, the ferrules 8 slip relative to the drive shaft 6 because both the drive shaft 6 and the ferrules 8 are made of steel. The rotation of the drive shaft 6 is thus not completely transmitted to the rotating arm 10, and the wafer platen (not shown) is oriented inaccurately by the rotating arm 10.
FIG. 2 is a graph showing encoder values and surface resistance values of a drive motor for controlling Y-axis tilt, by date, using the connecting system shown in FIG. 1. Reference numerals 21 through 23 designate plots showing the distribution of the surface resistance values against the angle of the ion beam for finding the encoder values of the drive motor corresponding to the zero point of the Y-axis tilt. Reference numerals 31 through 33 designate plots showing the distribution of the surface resistance values against the angle of the ion beam when the drive motor was operated under encoder values corresponding to the zero point of the Y-axis tilt. Reference numerals 41 through 43 designate plots showing the distribution of the surface resistance values against the angle of the ion beam for finding the encoder values of the drive motor corresponding to the zero point of the Y-axis tilt, after the drive motor had been operated for a certain period of time.
First, on April 2nd, an encoder value xe2x88x9264.61 mm of the drive motor was finally obtained through first (21), second (22), and third tests (23) in order to establish the zero point of the Y-axis tilt. The absolute value of the surface resistance at an angle of xe2x88x921xc2x0 of the ion beam is similar to the absolute value of the surface resistance at an angle of +1xc2x0 of the ion beam on the plot 23, yielding encoder values suitable to set the zero point. Here, the surface resistance values are symmetrical about the angle of 0xc2x0 of the ion beam.
On April 30, the surface resistance values at an angle of xe2x88x921-+1xc2x0 of the ion beam were compared through first (31), second (32), and third tests (33) after the encoder value of the drive motor, in which the zero point had been set, was set to xe2x88x9264.61 mm. However, as the tests, showed, the absolute values of the surface resistance were not symmetrical about the angle of 0xc2x0 of the ion beam. Thus, the angle of the ion beam was determined to vary even though the drive motor was operated by the same encoder values.
On May 4th, encoder values of the drive motor were obtained through first (41), second (42), and third tests (43) when the absolute values of the surface resistance were symmetrical about the angle of 0xc2x0 of the ion beam. The encoder values of the drive motor obtained through these tests were xe2x88x9265.85 mm, xe2x88x9265.05 mm, and xe2x88x9265.15 mm, which are different from the encoder value xe2x88x9264.61 mm of the drive motor in which the zero point was first set. Thus, it was apparent that the connection between the drive shaft and the rotating arm in the system for controlling the Y-axis tilt was creating a problem.
FIGS. 3 and 4 illustrate a drive system for controlling the X-axis tilt in an ion implanter according to the prior art. Referring to these figures, the drive system includes rotary shafts 53 and 59, drive and follower pulleys 51 and 57, a belt 65 wrapped around the pulleys 51 and 57, spacers 63 and 73 spacing the shafts 53 and 59 from the pulleys 51 and 57, respectively, and nuts 61 and 71 for tightening the spacers 63 and 73. Reference numeral 67 designates a boss of the follower pulley 57.
The rotary output of a drive motor is transmitted to the follower pulley 57 by the belt 65. The rotary force of the follower pulley 57 is, in turn, transmitted to the rotary shaft 59 connected to the follower pulley 57 by the nut 61. The shaft 59 rotates a wafer platen connecter 69 for controlling the X-axis tilt (angle of the wafer platen). In this drive system, the follower pulley 57 will slip relative to the shaft 59 if the nut 61 becomes loose. Also, slip occurs between the shaft 59 and the spacer 63 because both the shaft 59 and the spacer 63 are made of steel. Accordingly, the drive shaft 53 does not completely transmit its rotary force to the shaft 59. Thus, the angle of the wafer platen (not shown) is set inaccurately by the shaft 59.
An object of the present invention is to solve the above-described problems. More specifically, an object of the present invention is to provide a mechanism in which a rotating body and a rotary shaft are connected in a tilt assembly of an ion implanter such that the orientation or tilt of a wafer platen can be accurately controlled with respect to the ion beam.
To achieve the above object, according to a first aspect of the present invention, the rotary shaft has a key way extending parallel to the longitudinal axis of the shaft and at least one internally threaded hole in an end surface thereof. The rotating body has a boss defining a protrusion, and a plurality of internally threaded holes in one side thereof. The protrusion forms a key that extends in the key way of said rotary shaft. An end cap is screwed to the rotary shaft and the rotary body via the internally threaded holes thereof to thereby join the rotary shaft and the rotating body.
The rotary shaft may be a drive shaft of a transmission mechanism for use in controlling the Y-axis tilt of the wafer platen, or may be a drive shaft or a follower shaft of a transmission mechanism for use in controlling X-axis tilt of a wafer platen. The rotating body may be a rotating arm of a transmission mechanism for use in controlling the Y-axis tilt of the wafer platen, or may be a drive pulley or a follower pulley of a transmission mechanism for use in controlling the X-axis tilt.
Preferably, the key way has the shape of a trench shape in which the bottom and sidewalls are perpendicular to each other. The rotary shaft preferably has only one internally threaded hole therein, the hole formed at the center of the end surface of the shaft. On the other hand, the rotating body preferably has six internally threaded holes. Whereas the rotating body is preferably formed of steel, the screws are preferably formed of SUS.
To achieve the above object, according to a second aspect of the present invention, the rotary shaft has a key way extending parallel to the longitudinal axis thereof, the rotating body has a boss into which the shaft extends and a plurality of internally threaded holes, at least one ferrule is interposed between the rotary shaft and the rotating body within the boss of the rotating body, a key extends into the key hole, a bracket has a supporting plate having a keyhole in which an end of the key is fitted and a pressure ring pressing against the ferrule, and an end cap covers the keyhole. Screws join the bracket and the end cap to the rotating body.
The rotary shaft may be a drive shaft and the rotating body may be a rotating arm of a transmission mechanism for use in controlling the Y-axis tilt of a wafer platen. The rotating arm is formed of steel.
Preferably, the key way has the shape of a trench in which the bottom and sidewalls are perpendicular to each other. The key has an end that preferably is spaced from the end of the key way within the rotary shaft. Also, the cross section of the keyhole preferably has the same shape and size as that of the key.
To achieve the above object, according to a third aspect of the present invention, the rotary shaft has a key way extending perpendicular to the longitudinal axis of the shaft in an end surface thereof, and the rotating body has a boss into which the shaft extends, and a plurality of internally threaded holes and a key way open at one side of the rotating body. A spacer is disposed in the boss of the rotating body as interposed between the rotary shaft and the rotating body. A nut tightens the spacer at the outside of the spacer. A key is fitted in the key ways of the rotary shaft and rotating body. An end cap contacts the key and is screwed to the rotating body via the internally threaded holes thereof.
The rotary shaft may be a drive shaft or a follower shaft of a transmission mechanism for use in controlling the X-axis tilt of a wafer platen. The rotating body may be a drive pulley or a follower pulley of the transmission mechanism, and the rotating body is formed of steel.
Preferably, the key way extends across the central axis of rotation of the shaft, and has a rectangular cross section. Also, the cross section of the key way of the rotating body preferably has the same shape as that of the key way of the rotary shaft, and the bottom surface of the key way of the rotating body lies in the same plane as the bottom surface of the key way of the rotary shaft. Still further, the widths of the key, the key way of the rotary shaft, and the key way of the rotating body are preferably equal, and the thickness of the key is greater than the depths of the key ways.
To achieve the above object, according to a fourth aspect of the present invention, the rotary shaft has a key way extending perpendicular to the longitudinal axis thereof in an end surface of the shaft, the rotating body has a boss into which the rotary shaft extends and a plurality of internally threaded holes at one side of the body, and the key way of the rotary shaft has bottom surface recessed within the side of the rotating body. A spacer is disposed within the boss of the rotating body as interposed between the revolving shaft and the rotating body. A nut tightens the spacer at the outside of the spacer. A key is fitted in the key way of the rotary shaft and extends therefrom. An end cap contacts the key and is screwed to the rotating body via the internally threaded holes thereof to join the key to the rotating body.
The rotary shaft may be a drive shaft or a follower shaft of a transmission mechanism for use in controlling the X-axis tilt of a wafer platen. The rotating body may be a drive pulley or a follower pulley of the transmission mechanism.
Preferably, the width of the key is equal to the width of the key way.
According to the present invention, a rotary shaft and a rotating body are integrated by at least a key so as to rotate as one, i.e., without slip occurring between the rotary shaft and the rotating body. Thus, an accurate ion beam angle is maintained. Also, the reliability of the ion beam implanter is increased, and fewer implanted wafers are rejected thereby increasing the productivity of the semiconductor manufacturing process.